Wireless devices or terminals for communication are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Wireless devices are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server, such as server providing video streaming service, via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, computers, or tablets with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
A cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area is served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. eNodeB (eNB), NodeB, B node, Base Transceiver Station (BTS), or Access Point (AP), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the wireless devices within range of the base stations. The base stations and wireless devices involved in communication may also be referred to as transmitter-receiver pairs, where the respective transmitter and receiver in a pair may refer to a base station or a wireless device, depending on the direction of the communication. Two wireless devices involved in device-to-device (D2D) communication may also be referred to as a transmitter-receiver pair. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to a wireless device. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the wireless device to the base station.
Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for communication with terminals. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission in LTE is controlled by the radio base station.
LWA
LTE-WLAN Aggregation (LWA) is a feature where a UE may receive and transmit using radio links to both an eNB and a Wireless Local Area Network (WLAN). It is part of 3GPP Release-13. In the split bearer architecture option, also denoted as 3C of LWA, the downlink data is split on the Packet Data Convergence Protocol (PDCP) layer in the eNB, 3C here and 2C below refer to option numbers in Release-12 TR for dual connectivity in 3GPP, TS 36.842. The eNB may route PDCP Packet Data Units (PDUs) dynamically via eNB Radio Link Control (RLC) to the UE directly, or via a backhaul channel to WLAN and then to the UE. In the separate bearer architecture, also denoted 2C, the lower layers of a bearer are switched to LTE or WLAN meaning that all PDCP packets of that bearer are routed via either LTE or WLAN side. FIG. 1a shows the protocol architecture for LWA wherein
RRC means Radio Resource Control
MAC means Medium Access Control
PHY means Physical layer
IP means Internet Protocol
The WLAN termination point in the network, denoted WT, may be implemented by a WLAN AP and/or Access Controller (AC) or any other network node. The interface protocol between eNB and WT is denoted Xw.
The following characteristics are described in 3GPP TS 36.300 Rel-13. Note that this is not a complete list:                E-UTRAN supports LWA operation whereby a UE in RRC_CONNECTED mode is configured by the eNB to utilize radio resources of LTE and WLAN.        The eNB supporting LWA is connected to WLAN via an ideal/internal backhaul in the collocated deployment scenario or a non-ideal backhaul in the non-collocated deployment scenario.        In the non-collocated scenario, the eNB is connected to a WT logical node.        The Xw User Plane (UP) interface (Xw-U) and the Xw Control Plane (CP) interface (Xw-C) are defined between eNB and WT.        The UE supporting LWA may be configured by the E-UTRAN to perform WLAN measurements.        The eNB provides the UE with a “mobility set”, i.e. a group of APs, e.g. by Service Set Identifier (SSID), Homogeneous Extended Service Set Identifier (HESSID) or Basic Service Set Identifier (BSSID), among which WLAN mobility mechanisms apply while still supporting LWA, i.e., the UE may perform mobility within a group of APs transparently to the eNB. UE mobility across such groups of APs is controlled by the eNB e.g. based on measurement reports provided by the UE.        